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GCN Circular 12658

Subject
GRB 111208A: Swift-XRT refined analysis
Date
2011-12-11T01:25:02Z (12 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
C. A. Wolf (PSU) reports on behalf of the Swift-XRT team:

We have analysed 4.5 ks of XRT data for the Swift/BAT ground-detected
burst: GRB 111208A (Sakamoto et al. GCN Circ. 12628), from 24.3 ks to
40.8 ks after the burst. The data are entirely in Photon Counting (PC)
mode.  An X-ray source is detected within the Swift/BAT error circle.
Using 4204 s of PC mode data and 6 UVOT images, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 290.22434, +40.67616 which is
equivalent to:

RA (J2000): 19h 20m 53.84s
Dec(J2000): +40d 40' 34.2"

with an uncertainty of 1.6 arcsec (radius, 90% confidence). This
position is 37 arcsec from the Swift/BAT position. 

The light curve can be modelled with  a power-law decay with a decay
index of alpha=3.14 (+0.23, -0.90).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.14 (+0.25, -0.37). The
best-fitting absorption column is  1.7 (+1.1, -0.9) x 10^21 cm^-2,
consistent with the Galactic value of 8.4 x 10^20 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 3.5 x 10^-11 (5.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 8.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.14 (+0.25, -0.37)

The results of the XRT-team automatic analysis are available at

http://www.swift.ac.uk/xrt_products/00020190
.

This circular is an official product of the Swift-XRT team.
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